Magnetic domain logic device

ABSTRACT

A magnetic device comprising a first and a second plate of a magnetic material between which domains are situated. An interaction force occurs between the domains in the two plates. Stable domain positions in a second plate define equally stable domain positions in a first plate. One or both plates can be provided with domain guiding structures. Domain displacement in one plate can control a domain displacement in the other so that a variation in the interaction force is produced.

This is a continuation of application Ser. No. 277,150, filed Aug. 2,1972, now abandoned.

The invention relates to a magnetic device comprising a first plate of amagnetic material in which at least one domain can be present. The saidplate has a preferred magnetization direction which extends transverseto the plane of the plate. The rare-earth and yttriumorthoferrites areexamples of materials which are suitable for this purpose. A said domainis an area in the plate which, if a field is applied transverse to theplate, has a magnetization which is opposed to the direction of theapplied field. As is known, such a domain can have different shapes suchas a circular or annular, strip-like etc. section.

A wide variety of proposals have been made so as to enable the use ofsuch domains. To this end it must be possible to influence the domain insome manner. For example, there must be a variable field or a rotaryfield to enable displacement etc. of a domain along a strip of permalloywhich is specially formed for this purpose. The invention has for itsobject to provide a very useful and simple extension of thepossibilities of externally influencing a domain. To this end, themagnetic device according to the invention is characterized in that asecond plate of magnetic material in which a domain can be present isprovided, at least the projection of said second plate covering at leastpart of the first plate, an interaction force occurring between at leastone domain in the first and one domain in the second plate.Consequently, this means that according to the invention domainsinfluence each other; it must be emphasized that these domains aresituated in different plates of magnetic material.

The plates will generally be arranged to be parallel with respect toeach other so as to ensure that the interaction between a domain in afirst plate and a domain which is present in a second plate directlythereabove or therebelow, is independent of the position of the domainsin the plate.

Consequently, in the exmples hereinafter always a parallel platearrangement is shown, even though the invention is not restrictedthereto.

This principle of influencing can be used in a wide field ofapplications. This influencing can be used particularly advantageouslyin magnetic devices in which domains are to be displaced.

A magnetic device of the kind set forth in which a domain guidingstructure is provided for displacing domains in the first plateaccording to a given trajectory according to the invention ischaracterized in that said second plate serves to create stablepositions for domains in the first plate by means of domains situated inthe second plate. It is to be noted that the use is known of an elementin the form of a second, in this case non-magnetic plate so as to createstable positions for domains in the first plate. However, this secondplate then does not contain domains but separate magnets which areprovided for this purpose in openings of the plate. It will be obviousthat the use of domains in the second, i.e. magnetic, plate according tothe invention offers advantages: domains can be readily generatedtherein and in principle no operations are required with or on theplate. This is because the domains will arrange themselves according toa given pattern in the second plate, depending on the number of domainsand inter alia the thickness of the plate, so that a stable pattern ofdomains is produced which creates the said stable domain positions fordomains in the first plate.

A further possibility of application of the principle of the inventionfor the displacement of domains is offered by a magnetic device which ischaracterized in that a domain guiding structure is provided in thesecond plate for displacement of domains according to a giventrajectory, these displaceable domains in the second plate definingdisplaceable stable domain positions in the first plate.

A magnetic device of this kind offers a very interesting and simplemethod of displacing domains. The first plate, or first plates sincethere can be more than one, can contain information which can bestationary and displaceable, without a domain guiding structure and, forexample, rotary or varying fields being required for this purpose. Thisis achieved by the presence of the said second plate according to theinvention in which the said domain guiding structure is present and inwhich the domains, arranged according to the trajectory of thisstructure, define stable domain positions in the first plate (plates).If the domains in the second plate are displaced, the correspondingdomains in the first plate (plates) are taken along. As the second platewill be completely filled with domains, the displacement of thesedomains can be very readily realized without a guiding structure of aspecial shape and special fields being required. For example, a furtherembodiment according to the invention is characterized in that thesecond plate is completely filled with domains along a guidingstructure, domains in the second plate being displaced via means whichexert a "pull-push" force on the domains, the displacement of domains inthe first plate being determined by said displacement of the domains inthe second plate. For example, the domain guiding structure can consistof a continuous strip of permalloy along which the domains travel, thedomains being subjected to an external pull-push force which isgenerated, for example, by current pulses in wire loops which areprovided at only one or at a few locations on the plate, theirdisplacement also being stimulated by their mutual repulsion.

Elaborating on the foregoing, a combination is also possible wheredomain guiding structures are present for displacing domains in thefirst plate along given trajectories as well as for displacing domainsin the second plate according to a given trajectory, a displacement of adomain in the second plate causing and controlling a displacement ofdomains according to one of the trajects in the first plate.

In particular with the latter configuration a magnetic device isobtained which is suitable for many purpose. The domains, displaceablealong given trajects in the first plate, can be controlled by thedomains in the second plate which are also displaceable along giventrajectories. It is thus possible to realize logic functions as will bedescribed hereinafter.

The dimensions of the domains in the said first and second plate aredetermined inter alia by the degree of influencing of a domain in thesecond plate by a domain in the first plate, and vice versa. Thisinfluencing is dependent on the distance between the two said plates atthe area of the relevant domains. This distance is in principle variablefrom zero to infinity, the influencing then being maximum and zero,respectively. This fact can be used to good advantage. To this end, afurther embodiment of the magnetic device according to the invention ischaracterized in that said first and second plate are displaceable withrespect to each other, the dimensions of the domains in the plates thusbeing variable. A dimensional variation of this kind can be used, forexample, for measuring distances, or variations therein, such asmechanical vibrations, by detection of said dimensional variation. Theapplicability, however, is wider still. This is because fieldvariations, wich occur between the two plates in the case of a saiddisplacement can cause domain displacements. A magnetic device accordingto the invention in which a structure for domain guiding is provided onat least one of the plates, consequently, is characterized in that saidfirst and second plate are displaceable with respect to each other, adomain being displaceable in the direction of such a guiding structureas a result of a dimensional variation of the domain.

It is important to note that there need not always be an interactionbetween one domain in the first plate and one domain in the secondplate, but that it is equally possible that an interaction existsbetween more than one domain in the first plate and one domain in thesecond plate, etc. A special example thereof is a device in which thesecond plate comprises a strip-like domain by means of which stabledomain positions are defined in the first plate at the area of theprojection of the ends of said strip-like domain.

The embodiments according to the invention are not restricted toconfigurations comprising only a single first and second plate, butthere can also be a plurality of first and/or second plates of magneticmaterial in which domains can be present. It is also to be noted thatthe thicknesses of the plates may differ. A second plate preferably hasa thickness which exceeds that of a first plate. This is due to the factthat the stabilizing effect provided by such a second plate is greaterin that case, so that a plurality of first plates can benefit therefrom.The same can be noted with respect to the distance between a first and asecond plate. In given cases this distance will be equal to 0.

This and other aspects of the invention will be described in detail inthe description of the Figures which will be given hereinafter and whichserves for the explanation of the invention.

FIG. 1 shows a domain in a first and in a second magnetic plateaccording to the invention,

FIG. 2 is a sectional view of the arrangement of FIG. 1,

FIGS. 3a .[.and.]. .Iadd.to .Iaddend.3f show a number of other feasibledomain shapes in one or more first plates and one second plate accordingto the invention,

FIGS. 4a and 4b show a plurality of domains in two plates and in morethan two plates, respectively.

FIGS. 5a and 5b show a magnetic device according to the invention inwhich a domain guiding structure for domains in the first plate isprovided,

FIGS. 6a, 6b, 6c and 6d show a magnetic device according to theinvention in which a domain guiding structure for domains in the secondplate is provided,

FIGS. 7 and 8 show magnetic devices according to the invention,comprising a domain guiding structure both for a first and for a secondplate,

FIGS. 9 and 10 show detailed domain guiding structures for use in theexample shown in FIG. 8,

FIG. 11 shows another example of a controllable displacement of domains.

FIG. 12 shows an example of a first and a second plate according to theinvention which are displaceable with respect to each other.

FIG. 13 shows an example of plates according to the invention which aredisplaceable with respect to each other, a domain guiding structurebeing provided for at least one of the plates.

The reference numeral 1 in FIG. 1 denotes a first plate of a magneticmaterial, and the reference numeral 2 denotes a second plate of amagnetic material. In plate 1 a domain 3 is present, and plate 2accommodates a domain 4. The plates have a preferred magnetizationdirection which extends transverse to the plane of the plates. Amagnetic field H extends from the top downwards, transverse to theplates. Domains 3 and 4 can be generated, for example, by means of acurrent-carrying loop. The stray field of the domains is denoted bylines of force 5. The stray fields of the domains 3 and 4 interact, theinteraction force occurring being larger as the distance between theplates 1 and 2 is smaller. It is to be noted that the dimensions of adomain in a plate are dependent on the thickness of the plate and thenumber of domains present in the plate. It is obvious that the saidinteraction force also influences the dimensions of the domains 3 and 4in plates 1 and 2, respectively, in devices according to the invention.

FIG. 2 is a sectional view of the arrangement of FIG. 1. It is shown howthe domains 3 and 4 have north poles and south poles (N - Z), so thatobviously mutual influencing exists, i.e. attraction occurs between thetwo domains in accordance with the shown configuration. If the domain 4has a properly defined position in plate 2, this domain 4 will create,when said force of attraction exists, a stable domain position in plate1, i.e. at the area where domain 3 is shown.

FIGS. 3a and 3f show a number of different feasible domain shapes inplates 1 and 2. The interaction occurs between domains which can haveany shape feasible for domains. In all cases shown a force of attractionexists between oppositely arranged domains. FIG. 3a shows a so-termedannular or hollow domain 6 and 7 in plate 1 and in plate 2,respectively, these domains being shown in a partly sectional view. Theinteraction also occurs between different kinds of domains in the twoplates. FIG. 3b shows, by way of example, an annular domain 6 in plate 1and a domain 4 having a circular section (according to FIG. 1) in plate2. FIG. 3c shows another example: in plate 1 an annular domain 6 isprovided and therein a domain 3 having a circular section, while inplate 2 a domain 4 is again provided. FIG. 3d also illustrates that theplates 1 and 2 can be situated at a distance from each other which isequal to zero (d=0). The interaction will then be large. FIG. 3e shows,by way of example, not one but two first plates 1 and 1'. In this casethe second plate 2 is provided between 1 and 1'. Domains 3 and 4 areshown, domain 4 notably exerting an influence on both domain 3 in plate1 and domain 3 in plate 1', thus creating stable domain positionstherein at the area of the domains 3.

It is to be noted that the general term domain is to be understood tomean explicity any shape of domains, such as domains having a circular,annular, strip-like etc. section,

FIG. 3f shows another example of a strip-like domain 8 in a plate 2.This does not result in one but two stable domain positions in plate 1,i.e. in this configuration at the area where domains 3 and 3' aresituated. As a result of the interaction, the stip-like domain 8broadens somewhat at its ends.

A configuration as shown in FIG. 3f is interesting as the length of thestrip domain 8 can be varied with the field transverse to the plates, sothat at the same time the distance between the domains 3 and 3' isvaried. This distance can now be many times smaller than in the absenceof the plate 2 since domains 3 and 3' in one and the same plate repeleach other. Another advantage of this configuration is that the distancevariation is effected by a very small field variation as the length ofthis strip was found to be very sensitive to a field variation.

FIGS. 4a and 4b show examples of a plurality of domains in a pluralityof plates 1 and 2. Moreover, the thicknesses of the plates aredifferent, by way of example. In particular, plate 2 is thicker than theplates 1,1', 1", 1'" and 1"" (FIG. 4b). This can be advantageous inpractice as the interaction can then readily be so large that in thefirst plate 1 domains can exist only at the areas where, viewed inprojection, domains are present in the second plate 2. It is thusprecluded that domains can also be present at other locations inplate 1. In FIG. 4a the plate 1 has domains 10 where domains 20 areprovided in plate 2. Plate 2 also comprises domains 21 above which thereare no domains in plate 1. This can be determined by the informationpattern present in plate 1. FIG. 4a also shows that the dimensions ofdomains 20 and 21 in plate 2 differ. This is dependent on whether or nota domain faces a domain 10 in plate 1 so that interaction occurs. Thisis also visible in FIG. 4b; in plate 2, being thicker than plates 1, 1',1", 1'" and 1"" and being arranged therebetween, the domain dimensionsof domains 20, 21 and 22 are also dependent on the presence or absenceof domains 10 in the various plates 1, 1', 1", 1'" and 1"". The FIG. 4bshows that, particularly in the case of a thick plate 2, a number ofthinner plates 1 can be "looked after" by such a second plate 2.Consequently, one second plate 2 can create stable domain positions in aplurality of first plates 1 (1', 1", 1'" and 1"").

As described any other feasible configurations can be used to goodadvantage in magnetic devices according to the invention where it isnecessary to displace domains.

A number of domain displacement means are known, for example, domainguiding structures in the form of patterns of wire loops through which apulse current is fed which takes along the domains from loop to loop, orstructures of permalloy in a variety of shapes (for example, T-bars orY-bars), where a magnetic field, rotating in the plane of a said plateof magnetic material, provides the transport of the domains, orstructures such as a so-termed angelfish structure in which a magneticfield of varying dimensions, extending transverse to the plate, providesthe transport of the domains in the direction of the structure. In givencases it is already sufficient to use strips of permalloy (tape-like)along which the domains are transported, for example, by means of asmall external field which is displaced. In the following examples useis made of the said means, which are not elaborated upon further than isnecessary for understanding the present invention. Domain guidingstructures are denoted in the examples by broken lines and may have anyknown shape.

In FIGS. 5a and 5b, FIG. 5b being a sectional view of FIG. 5a along theline A--A, a device is shown in which a first plate 51 comprises domains53 and a second plate 52 comprises domains 54. Moreover, the first plate51 comprises structures 55 along which the domains 53 can be transported(see above). Also provided are inputs 56 on which the domains 53 can begenerated or be supplied from elsewhere in known manner. Dischargingand/or detection of domains can be effected on the right hand side ofthe plate. This generation or supply can be determined by giveninformation which is transported or stored in the form of domains inplate 1. This results in a pattern of domains 53 in plate 51 which isgiven by way of example. The plate 52 according to the invention servesto define stable domain positions for plate 51. In this example plate 52is completely filled with domains 54 which are arranged according to aregular pattern. This can be readily achieved by creating a sufficientnumber of domains in the plate under given conditions, for example,field strength and plate thickness. The modulation of the magnetic fieldin which the plate is situated can be an aid in achieving this regularpattern. A stable domain position is defined in plate 51 above eachdomain 54 in plate 52. This means that, independent of small deviationsof the domain guiding structures on the plate 51 and also independent ofmaterial deviations (isotropic) in plate 51, a properly defined domainpattern of domains 53 can exist in plate 51. When these domains 53 aredisplaced, in which case the interaction force with a domain 54 has tobe temporarily overcome by means of the displacement means, thisdisplacement can be effected very regularly between the defined stabledomain positions. An interesting aspect is that different concepts arepossible under different circumstances. For example, if a deviceaccording to the invention serves exclusively for the transport ofinformation during given periods, it is possible to make the interactionbetween domains 53 and 54 disappear by making the domains 54 disappear.If such a device serves mainly as a storage device during anotherperiod, the plate 52 can be filled again with domains 54, and so on. Animportant advantage of this kind of arrangement is that it is possibleto operate without an external magnetic field (see field H in FIG. 1) asthe domains can maintain each other by interaction. A complete fillingas that of plate 52 in itself is very stable and the effect of the strayfield of each domain 54 on plate 51 is such that in this plate 51domains 53 can exist without a separate external magnetic field beingrequired.

FIGS. 6a and 6b show devices according to the invention in which a firstplate 61 comprises domains 63 and a second plate 62 comprises domains64, FIGS. 6c and 6d showing a feasible section along the line A--A ofFIG. 6b. In FIG. 6a plate 62 has a domain guiding structure 65 which isa closed loop for transporting domains 64 therealong. In this case thestructure 65 is completely filled with domains 64 which can circulatetogether along the loop. It is possible to make the domain guidingstructure simply on a permalloy strip (tape-like) and to effect thetransport therealong by a pull-push action. This can be readilyrealized, for example, by providing a number of wire loops 66, 67 at oneor more locations along the trajectory 65. A given pattern of pulsesthrough these groups will result in a forced transport of domains in agiven direction (see, for example "Electronics", Sept. 1^(st) 1969, page85). In the FIG. 6a the transport direction is assumed to extend to theleft.

If desired, the said loops 66 and 67 can also be provided at a pluralityof locations along 65. This trajectory 65, completely filled withdomains 64, creates, in as far as it is covered by plate 61,displaceable stable domain positions 63 in this plate 61. Thisdisplacement will then be effected according to a trajectory 68(stroke-dot line) which is the projection of traject 65 onto plate 61.Information in the form of domains 63 can then be applied to a point 69of plate 61. A bit 0 is then, for example, a domain 63, and a bit 1 isthe absence of a domain. As a result of the interaction between domains63 and domains 64, this information is thus transported on plate 61. Ifthe circulation of domains 64 in plate 62 is stopped at a given instant,the information in plate 61 stands still. Discharging or detection ofinformation can be effected on the righthand side of plate 61. In thisway a device for transporting and retaining information in the form ofdomains is realized which is very simple and which does neither requireany domain guiding structures of a special shape (T-bars, Y-bars etc)nor varying or rotating magnetic fields. Consequently, theinformation-carrying plate 61 does not even have to comprise a simpledomain guiding structure such as the guide trajectory 65 for plate 62.If the interaction is sufficiently large, it will also be possible toomit the main field for the magnetization (field H in FIG. 1) in such adevice. It is to be noted that other configurations in which, forexample, the information can be applied to a number of points 69 inknown manner and in which the trajectory 65 is subdivided into a numberof independent trajectories 65, are of course also possible within thescope of the invention.

In FIG. 6b (and 6c which is a sectional view) a slightly modified deviceis shown. This device comprises domain guiding structures 65' which arearranged in parallel on plate 62. On points 70 information in the formof "domain present" and "domain absent" (1-bit, 0-bit) is applied to thestructure 65' and is transported therealong. This means that in theplate 62 itself, defining the stable positions, a given informationpattern can be transported or stored. In plate 61 the domains 63 willtake in positions which result in the same information pattern.Consequently, the information in plate 62 is copied to plate 61. This isadvantageous in cases where information is collected in a plate 62,after which it must be applied to one or even more than one second platein one operation.

The said possibility of coyping is also useful in cases where, forexample, the magnetic material of plate 61 is quite suitable fordisplaying the information pattern, for example, by means of light, butnot very suitable for transporting the information also in the plate bymeans of domain displacement means. If the material of plate 62 is verysuitable for this transport with the aid of displacement means, but notvery suitable for the reading out or displaying of the informationpattern by means of light, a combination of two of such plates 61 and 62is useful due to the interaction forces occurring therebetween. Such acase can be illustrated as follows. A domain pattern can be made visibleby using the Faraday effect. A domain causes a rotation of thepolarization plane of transmitted light and detection of this rotationresults in an image of the domain pattern. It is known that the rotationof the polarization plane is large if a plate of magnetic material iscut at right angles to the optical axis instead of cutting such a platefrom a crystal at right angles to the preferred direction of themagnetization. The rotation of the polarization plane can thus be afactor 10³ higher as double refraction no longer occurs upontransmission of light. However, the behaviour of such a plate, in thiscase, for example, 61' in FIG. 6c which is obtained by a cutperpendicular to the optical axis, is different with regard to domainsthan that of a plate obtained by a cut perpendicular to the preferreddirection of magnetization. The domains 63' will be in a tilted positionand will be difficult to displace. If a second plate 62' (FIG. 6c) isobtained by a cut perpendicular to the preferred direction of themagnetization and the displacement of domains 64' therein by means ofstructures 65" imposes no problems, the displacement of the domains 63'in plate 61' can be realized by the interaction occurring from plate62'. This interaction can readily be so large, inter alia by choosingthe distance between the plates 61' and 62' to be small and the plate62' to be thicker, that the taking along of domains 63' in plate 61' bythe domain 64' in plate 62' is always ensured.

FIG. 7 shows an example of a device according to the invention in whichdomain guiding structures are provided for domains in a first as well asfor domains in a second plate. A first plate 71, and in this case alsoanother first plate 71', by way of example, has a structure 75, 75',respectively, along which domains 73 can be displaced. Denoted by thereference 76 is a supply/discharge location for domains. A second domain72 also has a structure, i.e. 77, along which domains 74 can bedisplaced. In plate 72, for example, the complete structure 77 isoccupied with domains, so that it creates stable domain positions forpositions along the guide structures 75 and 75' in the plates 71 and71', respectively, said stable domain positions also being displaceable.In plate 71 (71') a given information pattern is provided or is storedtherein. The following can be achieved by means of this configuration:if information is to be transported in plate 1, this can be effectedwithout rotating or varying external fields being necessary. The domainguiding structures 75 and 75' can be simple permalloy strips, specialshapes not being necessary. The reason for this is that information inplate 71, arranged in the form of the structure 75, can be taken alongby the displaceable domains 74 in plate 72. The complete pattern ofstable domain positions is thus capable, as a result of itsdisplaceability in plate 72, of performing a desired transport in theinformation-carrying plate 71 (71'). The displacement of the domains inplate 72 itself can then also be readily effected since the completefilling along a structure 77, which can also consist simply of straightstrips of permalloy, makes it possible to transport the domains 74 inplate 72, for example, by generating a domain each time at the beginning(78, for travel in the one direction) of such a structure and by makinga domain disappear at the end (78, for travel in the other direction) ofsuch a structure. The complete filling is thus shifted further in itsentirety. It is alternatively possible to provide the plate 72 with aclosed transport loop so that always the same shifting domains are used.See the description given with reference to FIG. 6a in view of theguiding trajectory 65 and the push-pull movement for the regularshifting of domains along a trajectory with a complete filling.

FIG. 8 shows an interesting example of the application of theinteraction between domains in a first plate 81 and a second plate 82. Adomain in plate 81 can be transported along a structure 85. Thestructure branches into two trajectories 85a and 85b. Assume that in thecase of a displacement a domain 83 would normally proceed from 85 to 85a(see hereinafter). Plate 82 comprises a domain 84 which is alsodisplaceable, in this case, for example, along a structure 86. Usingthis arrangement a domain 83 in plate 81 can be controlled by means of adomain 84 in plate 82. If domain 84 is in the position shown in FIG. 8,a domain 83 will follow the trajectory 85b instead of the saidtrajectory 85a. This is due to the fact that interaction occurs betweenthe domains 83 and 84.

FIGS. 9 and 10 illustrate such a branching of structures 85, 85a and85b, respectively.

FIG. 9 shows a T-bar structure along which a domain can be displaced, bymeans of a field rotating in the plane of the plate 81, along poleswhich are denoted by 1, 2, 3, 4, 1, 2, . . . . A domain 83 which issupplied at a will normally proceed from left to right to output a.b. Ifa domain 84 (shown in broken lines again in FIG. 9) in a plate 82 (notshown, compare FIG. 8) passes the branching point of the drawing fromthe top downwards, or is, for example, in the position shown, a domain83 is deflected and arrives on the output which is denoted by a.b. Inthis manner a switch is created for a series of domains. See furtherhereinafter.

FIG. 10 shows an angelfish structure. Due to a varying field whichextends transverse to the plane of a plate 81, a domain will normallytravel along 85 to 85a. The element 87 of the structure is somewhatasymmetrical, i.e. a point 87b is smaller than point 87a. A domain willnormally move via point 87a, but of a domain is present in the vicinityif point 87b, i.e. in particular not on the side of 87a in a plate 82(see FIG. 8), this domain will ensure that the domain in plate 81 istransported further in the direction of the structure 85b.

It will be obvious that logic functions can be realized using such aform of control of domains. This follows immediately from the drawing ofFIG. 9; for example: provided are an input a, and outputs a.b. and a.b.It is thus indicated that by means of this configuration (FIG. 9 inrelation with FIG. 8) two logic operations can be realized, i.e. a.b.and a.b. This follows from: if a domain 83 arrives at input a, thisdomain will arrive at output a.b. only if said domain 84 in the secondplate 82 arrives at or passes the position underneath plate 81 shown inFIG. 9. This represents the function a.b. if said presence of domain 84is denoted by b. If no domain 84 arrives, i.e. "not present", so b,domain 83 in plate 81 moves from input a to output a.b. This means thatthere is a, but not b: a.b.

It is to be noted that structures as shown in FIG. 9 and 10 are notnecessary if an arrangement is chosen where the plate 81 is arrangedbetween plates 82 and 82'. See FIG. 11. A domain 84 in plate 82,travelling along a structure 86, sends a domain 83 in plate 81 to oneside, and a domain 84' in plate 82' travelling along a structure 86'sends a domain 83 in plate 81 to the other side. In this case apermalloy conductor 85 (a.b.) already suffice; this conductor need nothave a special shape and no varying or rotating field is necessary.

FIG. 12 shows an example of two plates 111 and 112 according to theinvention which are displaceable with respect to each other. Plate 111is mounted, for example, on a component 115, the displacements of whichwith respect to a component 116 have to be measured. A domain 113 inplate 111 and a domain 114 in plate 112 influence each other. Thedimensions vary in accordance with the variation of the distance dbetween the plates 111 and 112. A wire loop 117 at the area of domain114 can serve for conversion of the dimensional variation into anelectrical signal. If a permalloy foil is provided at the area of, forexample, the domain 114, it is also possible to measure the electricalresistance of the permalloy so as to detect the dimensional variation ofthe domain which causes the resistance variation.

Other applications are feasible, for example, in the conversion ofacoustic vibrations into electrical signals etc. The reverse operationis of course also possible. In that case the plate 111 can be put intomotion by a variation of the dimensions of the domain 114 by a currentvariation in, for example, a wire loop 117 and hence by a variation inthe interaction force between domains 113 and 114.

FIG. 13 shows another example of plates according to the invention whichare displaceable with respect to each other. Plates 121 and 122 aredisplaceable with respect to each other. A domain 123 in plate 121 isdisplaceable along an angelfish structure which is given by way ofexample. Plate 122 comprises domains 124 which, by way of example,completely fill the plate 122 (compare plate 52 of FIG. 5). As a resultof the displacement of the plates with respect to each other, notablytransverse to the planes of the plates, the dimensions of domains 123(and 124) will vary. Using this dimensional variation, a domain 123 isdisplaced in this example in the direction of the angelfish structure.

It is to be noted that the displacement of the plates with respect toeach other need not be exclusively transverse to the plane of theplates. A displacement in the plane of the plates also produces avariation in the interaction between domains in a first and a secondplate. Applications involving operation in a corresponding manner canthus also be realized.

What is claimed is:
 1. A magnetic device comprising a first plate of amagnetic material in which at least one domain is present, a domainguiding structure having a plurality of continuous branched connectingpaths for the displacement of the domain in the first plate, a secondplate of magnetic material in which a domain is present, said secondplate covering, at least in projection, at least a part of the firstplate, an interaction force occurring between at least one domain in thefirst and one domain in the second plate, and a domain guiding structurehaving at least one path for the displacement of a domain in the secondplate which controls the displacement of the domain in the first platealong one of saaid paths therein.
 2. A magnetic device as claimed inclaim 1 including means to vary the distance between the plates wherebythe dimensions of the domains can be varied.
 3. A magnetic device asclaimed in claim 1 including means to vary a dimension of a domain inthe second plate whereby the domain is displaceable in the direction ofthe guiding structure. .Iadd.
 4. A magnetic device comprising a firstplate of a magnetic material in which at least one domain is present, adomain guiding structure having a plurality of guiding paths for thedisplacement of domains in the first plate, and a second plate ofmagnetic material completely filled with domains, said second domaincovering, at least in projection, at least a part of the first plate, aninteraction force occurring between at least one domain in the first andone domain in the second plate, the domains in the second plate creatingstable positions for the domains in the first plate. .Iaddend. .Iadd.5.A magnetic device as claimed in claim 4 including a domain guidingstructure for displacing domains in the second plate according to agiven trajectory, said displaceable domains in the second plate definingdisplaceable stable domain positions in the first plate. .Iaddend..Iadd.6. A magnetic device as claimed in claim 5 wherein the guidingstructure in the second plate is a closed loop. .Iaddend. .Iadd.7. Amagnetic device as claimed in claim 4 including domain guidingstructures for displacing domains in the first and second plateaccording to given trajectories, a displacement of a domain in thesecond plate causing and controlling a displacement of domains accordingto one of the trajectories in the first plate. .Iaddend. .Iadd.8. Amagnetic device as claimed in claim 4, wherein said first and secondplate are displaceable with respect to each other so that the dimensionsof the domains in the plate can be varied. .Iaddend. .Iadd.9. A magneticdevice as claimed in claim 4, including a structure for guiding domainsin at least one of the plates, and said first and second plate aredisplaceable with respect to each other, a domain being displaceable inthe direction of said guiding structure as a result of a dimensionalvariation of a domain. .Iaddend. .Iadd.10. A magnetic device as claimedin claim 4 wherein the second plate comprises a strip domain by whichstable domain positions are defined in the first plate at the area ofthe projection of the ends of said strip domain. .Iaddend. .Iadd.11. Anapparatus using magnetic bubble domains comprising:a first magneticmedium containing a lattice of magnetic bubble domains; and a secondmagnetic medium containing an information bit pattern of bubble domainsand the absences of bubble domains, said second magnetic medium beingarranged near and over the first magnetic medium so that the bubbledomains in the second magnetic medium are magnetically coupled to bubbledomains in the first magnetic medium, movement of the lattice of bubbledomains in the first magnetic medium thereby causing movement of theinformation bit pattern of bubble domains in the second magnetic mediumby said magnetic coupling. .Iaddend. .Iadd.12. An apparatus usingmagnetic bubble domains, comprising:a first magnetic medium andconfinement means for confining domains therein in a two-dimensionallattice of interacting bubble domains, the interdomain spacings in saidlattice being substantially determined by interactions between saiddomains and by said confinement means, a second magnetic medium, meansfor producing an information bit pattern of bubble domains and voids insaid second magnetic medium in positions where said bubble domains insaid second magnetic medium are magnetically coupled to bubble domainsin said first magnetic medium, the spacings between said bits in saidsecond medium being substantially determined by the interdomain spacingsin said lattice, means for moving said bubble domains in saidinformation bit pattern, comprising further means for moving domains insaid lattice to thereby move said information bit pattern of domains bysaid magnetic coupling, and means for sensing said bubble domains insaid second magnetic medium. .Iaddend. .Iadd.13. An apparatus usingmagnetic bubble domains, comprising: a first magnetic medium and aconfinement means for confining a two-dimensional lattice of columns ofmagnetic bubble domains therein, the positions of bubble domains withinsaid lattice being substantially determined by interactionstherebetween, and by said confinement means, a second magnetic mediumwith a coded pattern of magnetic bubble domains therein which aremagnetically coupled to domains in said lattice, each said domain insaid coded pattern being coupled to a different one of said domains insaid lattice, means for moving columns of bubble domains in saidlattice, to thereby drag columns of magnetically coupled bubble domainsin said coded pattern, means for producing said coded patten of bubbledomains in said second magnetic medium, means for sensing bubble domainsin said coded pattern of bubble domains. .Iaddend.